The present invention relates generally to communication channel quality monitor systems, and more particularly, to monitoring systems for indicating the intended values of signals in the communications channel if uncorrupted by noise and for indicating the extent of any such corruption occurring. Specifically it relates to an apparatus, which would be suitable for use in such a monitor system, which determines when the amplitude of a signal provided thereto crosses a preselected value, and the direction of that crossing.
Communication channels can be entirely analog extending from the information source to the transmitter, and then along the channel link to the receiver, and finally to the user of the transmitted information. Communication channels can also be digitally based, either totally or partially. A typical situation is to have a digital information source but where the information is sent over an analog channel link to a receiver which reconverts the information to a digital format.
Digital communication channels or communication channels having digital portions along the channel, i.e. digitally based communication channels hereinafter, are designed to have as large a tolerance for noise and other signal degradations as practicable. Such a system can have so large a designed-in tolerance that the system will operate substantially error free even though one or more elements thereof comes to operate in a severely degraded manner.
A major objective of performance monitoring is to detect such element degradation before corresponding errors are introduced, to thereby permit corrections or other expedients to prevent any such errors before they begin to occur in the communications channel. In a system for providing such performance monitoring of digitally based communication channels, a device may be needed for determining the times at which the amplitude of the incoming signal crosses a preselected level and whether the signal level is rising or falling at the times of those crossings.